Fire-resistant wall and ceiling structure



3 Sheeis-$heet 1 ll 1r, I! 7 {MES 2 |II|WHI 11 \HWJHLP HHV {1.4: & izi 1 1. 8 2 F Y Dec. 5, 1933. c. K. RQQffi FIRE RESISTANT WALL AND CEILING STRUCTURE Filed March 15, 1935 Dec 5, 1933.

c. K. Roos 1,938,354

3 Sheets-Sheet 2 Filed March 15, 1933 c. K. Roos 1,938,354

FIRE RESISTANT WALL AND CEILING STRUCTURE Filed March 15, 1953 s Sheets- Sheet 3 Ema Patented Dec. 5, 1933 FEE-RESISTANT WALL AND CE ILING STRUCTURE Carllsle K. Boos, Wheaton, m, assignor t6 United States Gypsum Company, Chicago, I l1., a corpoe ration of Illinois ApplicationMal-ch 15, 1933. Serial No. 660,873

20 Claims. (01. 72-124) This invention relates to fire-resistant wall and ceiling structures and plaster-board lath therefor, for use in dwellings and buildings havin plastered walls and ceilings where the rigid requirements of building codes and ordinances must -be met and at the same time a satisfactory construction at low cost must be provided.

While the building codes of large cities diifer somewhat in their requirements, it is generally 10 regarded that a wall structure which will pass the fire tests of the American Society for Testing Materials will satisfy the requirements of the several codes and ordinances. These tests require the subjection of the structure to the rigid conditions which it is assumed will prevail in case of a severe fire in a room where the structure is installed. The Bureau of Standards at Washington, as well as other bodies throughout the country, make such tests, and the structure of this invention has successfully passed those of the Bureau of Standards.

In the attempts heretofore made to provide structures to comply with these requirements, some of which, such as the metal-lath constructions, have been successful, their high cost prohibits their general use and for the average home or building they are not used.

The usual plaster-board construction, which has many advantages and has come into general use to replace the old wood lath type of construction, involves a plain, fiat, paper-covered plaster-board or lath consisting of a laminated sheet comprising a core of cementitious material,

such as set calcined gypsum, with covering sheets of a fabric such as heavy paper, which lath are nailed or secured to the studding, and a layer of plaster, consisting essentially of set calcined gypsum, is then applied directly to the face of the lath.

fibers of the paper covering of the lath and the whole presents a mechanically strong and satisfactory wall structure for ordinary purposes' When, however, such a wall structure is subjected to a high temperature for a prolonged time, such as the above-mentioned tests require, the heat calcines the plaster, beginning at the outer surfaces and progressing inwardly but at a reduced rate by reason of the fact that the heat required to dehydrate or calcine the gypsum tends to prevent further rise of the temperature of the plaster until its calcination is completed. Since calcined plaster is a good heat insulator,

an appreciable time is required before the cal- 5 cination reaches the stage, and the plaster reaches the temperature, at which any effect on the paper or fabric of the plaster-board is noticeable. As the temperature rises to the ignition point, the .paper or fabric would' ordinarily burst into flame, but by virtue of the covering of the co calcined plaster access of atmospheric oxygen to the paper or fabric is prevented, with the result that only a sort of dry distillation takes place. This dry distillation results eventually in the charring or carbonization of the paper or fabric, converting the same into a more or less coherent layer of carbon, which in itself hasfire-resistance value. But with the main supporting strength of the bond between the plaster and the paper or lath destroyed, the plaster cannot long support and sustain itself in position on the wall and soon falls exposing the lath which in turn rapidly fails and the fire breaks through, so that, with this plain lath type of construction, the wall cannot pass such tests despite its inherent fire- .75 resistant qualities.

As long, however, as the covering of the calcined plaster can be maintained in place upon a sufiiciently large area of the unbroken carbonized paper or fabric, the fire will not penetrate the wall. But calcined plaster is weak and the problem is how to maintain it in place for the required time. It is, however, more or less coherent, and advantage is taken ofthis, to provide a suitable key or lock to hold the plaster in position.

This is accomplished through the provision of a paricular kind of perforated plaster-board lath in which the perforations, their size and depth and their spacing have all been coordinated and correlated to the other characteristics of the board and structure, whereby the desired object is accomplished. These perforations in the lath are of such size that, when used on either a side wall or ceiling, the plaster will completely fill the same in the normal act of plastering to form the bodies of the keys, rivets or locks and so that, without excessive droppings on a vertical wall, they will protrude at the back of the board sufiiciently to form heads to bind and lock the layer of plaster to the lath. It is important'that the size of the keys bear such a relationship to the entire wall and ceiling structure that calcination -of the gypsum or plaster of which they are composed will be retarded for as long a time as possible. In order to accomplish these results it has been found that, if these rivet-like keys or locks have the greatest thickness relative to the thickness of the entire structure that is possible in View of other conditions, their calcination will be retarded for a considerable period beyond that of the plaster coating, thus enhancing the over-all fire resistance of the structure of which they form a part.

The problem also arises of determiningthe number of perforations and their spacing and their correlation with the other characteristics of the board and structure. It would ord arily be assumed that the greater the number of such perforations the greater the fire resistance would be, but careful consideration, plus tests and research, has determined that there is a limit to the number of perforations, and that if this limit be exceeded the fire resistance of the structure is diminished and eventually is definitely less than that of the plain plaster-board lath construction. One reason for this is that the board itself will then, of course, contain less paper facing on the fire side than if there were no perforations, and there will therefore be less carbon to resist the fire and smaller unperforated carbon forming areas.

Furthermore, a board containing too many perforations is weakened and cannot stand the strains to which it is subjected; moreover, with such board there is much breaking in handling and applying, and if there are too many perforations there will be a great increase in the amount of plaster required and in the labor in applying it, so that the structure becomes uneconomical.

As before stated, the perforations must be of such size and formation that the plaster will completely fill the same to form the bodies of the keys or looks in the normal act of plastering and without conscious effort by the plasterer, and so they will protrude at the back of the lath to form the heads, and this without substantial droppings in case of a vertical wall and without excessive extrusion when used on a ceiling. If the perforations are too large, excessive droppings occur and the falling heads take with them parts of the bodies of the keys, reducing their efficiency. On the other hand, if the holes are too small they cannot be filled with- -'solidplaster without extra pressure by the workman and are therefore apt to be imperfect, they are more quickly calcined, and readily crack and give way under the application of prolonged high temperature.

Moreover, the perforations cannot be too far apart or the holding and supporting effect of the interlock or rivets on the plaster is diminished and in the case of fire some of the calcined plaster will fall away in the larger spaces between interlocks, allowing direct access of oxygen to' the highly heated carbon, with the result that it burns away and allows access to the core of the plaster-board lath, which, in turn, becomes calcined and eventually the paper on the other side of the board is also burned-away. When this takes place, holes are formed through which the flames have access to the studding or other supports, and then it is a matter of only a short while before the structure falls, because of the lack of support after the studding or supports have burned away. But by properly coordinating the thickness of the plaster-board, the size of the interlocking keys, their depth andspacing, a wall and ceiling structure having the maximum obtainable fire resistance and strength is produced. There is a balance between the imperforate areas of the board, the size of the perforations and their spacing whereby the desired results are obtained.

Other considerations in spacing the perforations to be taken into account for best results are that the studding or other supports should not occur back of the perforations, which would prevent the plaster from passing through and forming heads on the rivets or keys at the back of the lath, since their holding power would thereby be measurably lessened and to that extent spots of larger areas of less protected plaster would occur in the surface of the structure. Since a wall and ceiling structure as a whole is no more fire-resistant than its weakest part, the proiected areas should be uniform.

Likewise, the perforations should not be too close to the edges of the lath or the lattter would be unduly weakened. rendering it less satisfactory in use, and causing breakage in handling. The arrangement, also, of the perforations preferably should be symmetrical in each lath, so that when they are installed the wall surface as a whole will be protected uniformly in substantially equal areas. And since it is desirable that the lath require as little care and attention as possible in being placed in position and be proof against improper positioning, the perforations preferably should be located symmetrically with reference to the edges of the board as well as in the interior thereof, so that no matter how the lath are placed in position in the normal way on the wall the perforations will be uniformly disposed over the entire wall.

These perforations in the plaster-board lath are preferably of smooth bore throughout the paper and core, whereby the surrounding paper and core of the lath are not torn or crushed or otherwise injured and their supporting functions not impaired. This is preferably accomplished by suitably drilling the perforations after the lath are otherwise completed, and preferably as they come from the drying kiln of the plaster-board machine and are assembled into bundles, such as are customarily sold to building-material deall ers, and all the holes in a bundle are preferably drilled at one operation by a suitable machine.

It is, therefore, an object of the invention to provide a plaster-board lath having comparatively few relatively large perforations therethrough and in which the size and distribution of the perforations are so related to the dimensions of the board, the imperforate areas, and the heat resisting and strength characteristics of the lath as to produce a perforated lath of maximum strength at moderate cost and which, when assembled into a wall or ceiling, will provide a structure which will successfully meet all standard flre tests: also whereby convenience and speed in the application of the lath to suitable standard spaced f a considerable period of time after the calcination of the plaster coating whereby they continue to support the calcined plaster coating in position on the structure for a comparatively long time after the paper surfaceof the lath has carbonized and the bond over the imperforate areas substantially destroyed.

I also provide a plaster board lath having a set cementitious core between sheets of fabric and having clean-cut, smooth bore perforations Loo formed without tearing or distorting the paper, or crushing or rupturing the core.

Further objects and advantages will be apparent from the specification and the appended claims. I In the drawings which illustrate a preferred embodiment of the invention:

Figure 1 is a perspective vertical sectional view of a portion of a double wall structure at the juncture of the vertical wall and ceiling, the section being taken through the perforations and keys therein.

. Fig. 2 is a face view of the structure with the plaster omitted from a portion thereof and showing the plaster-board lath as applied to the studding or other supports. This view shows a preferred symmetrical arrangement of the perforations and related unperforated areas.

Fig. 3 is a transverse section through one of the plaster-board laths, the section being taken through a row of perforations.

Fig. 4 is a substantially full size vertical sectional view through a completed single wall of the juncture of the side wall and ceiling, and is taken through the perforations and the keys therein.

Fig. 5 is a perspective view of one of the completed bundles of lath after the perforations have been drilled therethrough and illustrates the method of binding a plurality of, unperforated lath together into a bundle for transportation or storage, whereby the drilling operation may be accomplished after the bundle is formed.

Fig. 6 is a front elevation of a portion of a multiple spindle drilling machine in which all of the holes in each bundle of lath are drilled in a single operation.

Fig. '7 is a transverse section taken on a line.

corresponding to line 'l-'-7 of Fig. 6 and illustrates the drilling device in detail and the method of guiding the drills through the bundles of plaster= board lath.

Fig. 8 is an enlarged detail fragmentary view of a portion of the device as illustrated in Fig. 7. This view is drawn substantially to scaleand particularly illustrates the type of drill, the method of clamping the bundle and guiding the drill.

In the embodiment illustrated, particularly in Figs. 1, 2, and 4, the wall structure comprises a particular type of plaster-board lath 1 which is nailed to suitable studding 2 and to ceiling supports such as the joist 3, and the plaster 4 which is applied to the surface of the plasterboard.

It is standard practice to space the studding 2, or suitable supporting strips used for the same purpose, on sixteen inch centers, and the plasterboard lath l is therefore preferably made 48 inches long and 16 inches wide so 'that the verticaljoints between the ends thereof may be placed in staggered relation similar to that illustrated in Fig. 2. By this construction and method of positioning the boards relative to each other, there will always be the width of at least two boards between the vertical joints thereby strengthening the wall structure.

and extends f r a short distance underneath the other paper sheet 6 which is cemented thereto,'the cementitious material of the core squeezing outwardly between the in-turned edge and the sheet 6 during the process of manufacture. This provides an eflicient and uniform binding over the entire longitudinal edge and considerably increases the strength and efllciency of the board.

The lath are provided with a plurality of perforations 9.

The plaster, which is indicated as a whole by the reference numeral 4, comprises a comparatively thin scratch coat 10 which is first applied to the plaster-board and which is. indicated in Fig. 4 by heavy section lining. The scratch coat 10 is applied by the usual plastering method, and the size of the perforations 9 is such that they are completely filled with plaster to form a key or plaster-retaining means 11 therethrough. This plaster key by the normal operation of plastering is forced completely through the opening to form a head not such size as to bend downwardly as shown on the side wall or to mushroom as shown on the ceiling in a manner to assist in retaining the plaster in position.

Whenthe scratch coat 10 is sufficiently dried, a second coat 13 is applied which is preferably of the same material as the scratch coat and coheres perfectly therewith to form a substantially integral layer of plaster. A finishing coat 105 14 may be applied to the surface, if desired. The entire plaster coating 4, which is made up of the scratch coat, a second cpat, and the finishing coat, if desired, is substantially one-half inch thick. The size of the perforations and the keys 110 formed therein bear a suitable relation to the thickness of the plaster-board, the plaster coat 4, and the area between adjacent holes.

As a result of the various considerations and requirements, and a large number of experiments 115 and tests, I have discovered that with standard %-inch thick plaster-board lath, with a perforation on the order of inch in diameter for each 16 square inches, or thereabouts, of the board area, I am enabled toproduce a lath and wall structure capable of meeting the. requirements of the Bureau of Standards tests, and others referred to, as well as meeting all other requirements relative to convenience in handling, application, storage and transportation and without materially increasing the costof either the lath or the completed wall structure. The standard plaster-board lath being 48 inches long and 16 inches in width, the perforations are pref erably arranged in rows on 4-inch centers and 2 inches from the edges of the board all around.

By providing a A-inch hole in the %-inch board, and assuming the ordinary layer of plaster on the board to be about inch thick, the keys; rivets or interlocks produced in plastering will be about V inch in thickness as measured from the front of the finished plaster surface to the rear or obverse side of the plaster-board lath; Taking the rate of calcination of the plaster itself as a unit, it will take at least twice as long to calcine through to the back of the interlocks as it will take to calcine the plaster surface itself. However, in actual practice, and by virtue of the heat-insulating qualities of the calcined plaster, the rate of calcination drops off 145 rapidly as it pentrates into the keys, or interlocks, with the result that these keys will maintain themselves in uncalcined condition several times as long as the plaster surface itself. At the same time, by having a 4-inch center spacing, 150

effectiveness of this bond as the fire progresses is greatly prolonged and enhanced by the still uncalcined keys or interlocks which are still holding out against the effects of the coniiagration and hence providing an effective bar against the fire and preventing it from penetrating to the studs and into the intramural spaces.

The heat insulating layer of carbon protects the core of the lath and the core gives off its moisture to the keys through the comparatively large area of the walls of the perforations, thereby materially delaying their complete calcination and preventing access of atmospheric oxygen to the carbonized paper area between the perforations and in this way lengthening the life of the entire structure.

By the preferred spacing of the perforations or its equivalent, there is a symmetrical distribution, with respect to the keys, of the area to be pro-. tected in the bonding of the plaster-board as well as a symmetrical load distribution. The perforations are not closed at the back by studding on 16-inch centers, the standard distance, or on 12- inch centers, nor by any studding spaced a multiple of the distance between the perforations. The perforations are at a suitable distance from the edges of the board to prevent harm. to the latter either by drilling or later by handling, or by weakening the edge portions. The longitudinal bound edges of the lath are not interfered with. The perforations are sufficiently large to provide keys of sufiicient strength for their supporting and holding functions, as well as to retard calcination. At the same time they are not so large and numerous as unduly to weaken the board or permit waste of plaster by excessive droppings, nor do they require extra effort on the part of theplasterer or an excessive amount of plaster to fill them.

A series of careful tests on actual commercial building constructions have shown that with this perforated lath only between 5% and 6.15% more plaster is required than with plain lath, and this is so small anamount that it does not prove to be a commercial handicap or interfere with the ready sale of the product to the trade, particularly when consideration is taken of the remarkably improved fire resistance of the finished walls.

The perforations are also of a suitable size and spacing and arrangement so that the same lath may be used on either the side-wall or ceiling or on slanting walls or ceilings and, besides providing suitable keys, will meet all other necessary requirements in each case and under all practical conditions.

In this wall structure the plaster-board lath 1 are preferably secured to the studding 2 by suitable nails 15 and, in the arrangement shown in Fig. 2, the vertical joints on any one studding are always spaced by the width of two lath, that is, they are always at least thirty-two inches apart, which provides for the alignment of only a minimum number of vertical joints 18 on any one studding. This method of mounting, together with a minimum number of perforations in the plaster-board, and their size and symmetrical arrangement, provides a wall of martimum strength and efficiency, and capable 'of meeting all other requirements. 7

The plaster-board lath preferably are manufactured in the usual manner without perforations and may then be formed into bundles 17, as illustrated in Fig. 5, as is common. Such bundles have a paper binding 18 applied over each longitudinal edge of the bundle and slightly overlapping the top and bottom lath, as indicated at 19. These overlapping portions are secured with a suitable adhesive to the top and bottom lath only while the bundle is under pressureand all of the lath in the bundle are thus snugly held together and in alignment thereby.

The perforations in the lath should have smooth parallel sides for ease in filling with plaster in the act of plastering and to fully meet other requirements and with no crushed or broken surrounding core parts to impair their supporting functions or the holding effect of the keys, and the fabric covering should be cleanly cut to the diameter of the perforation. For this purpose, I prefer to form the perforations by drilling, and I provide a particular type of drill therefor; and

in order to drill at least one bundle at a time, a

drilling machine is provided whereby all the holes in all of the lath in a bundle may be drilled simultaneously and with one operation of the machine. This drilling machine, as shown in the drawings, comprises a stationary head 20 having multiple spindles therein to which suitable drills 21 are secured. The head 20 and the spindlesand drills therein are stationary, and a table 22 is positioned thereunder. This table 22 comprises, a perforated top 23 having a plurality of holes 24 therein, which are spaced in accordance with the desired distribution of the perforations in the plaster-board lath. The table 22 is vertically movable and may be raised upwardly, as shown in Fig. 6, to allow the drills to perforate all of the lath as indicated in dotted lines, or may be lowered to withdraw the drills, as indicated in Fig. 7. V The vertical movement of the table 22 may be accomplished by any suitable means, such as a hydraulic cylinder having a piston therein and suitable control means therefor. In order that the plaster-board lath bundles 17 may be easily moved onto or off the table, a plurality of shafts 25 are transversely mounted under the table top 23 and provided with rollers 26. These rollers are preferably of resilient material, such as rubber, and extend upwardly-through suitable openings 27 and slightly above the surface of the table top. A top presser plate 28 is slidably mounted on ertical guide rods 29. and compression sprin s 30 are mounted on the rods whereby the presser plate 28 will be normally retained in its lower position on the rods 29 but may be raised by pressure. The presser plate 28 is also provided with a plurality of holes 31 arranged to correspond with the position of the holes to be drilled in the plaster-board lath and in alignment with the holes in the table top 23. The presser plate 28 is provided with a cover 32 having holes therethrough for the passage of the drills and providing a chamber 33 to which suction conduits 34 are connected for the purpose of withdrawing any of the material from the plaster board which is brought through the presser plate bythe drills. The bundle of lath is thus compressed between these two presser plates and the intermediate faces of the lath brought solidly together for purposes of drilling, whereby the entire bundle may be drilled as perfectly as a single lath.

The resilient rollers 26 which project slightly above the table' top 23 may be intermittently or otherwise power driven, if desired, so that when the table. The material of the rollers provides a frictional surface for engagement with the lath, and suitable resilience is provided in the rollers or in their mounting whereby the pressing operation will cause either suflicient distortion or downward movement of the rollers to allow the uniform engagement of the table by the bundle and uniform pressure to be applied thereto. I

The table 22 is provided with chambers 35 therein, having outlets 36 therefrom, which may be attached to suitable blowers to remove the material drilled from the perforations.

In order to insert the unperforated bundles on the table and between the table and the presser plate, the table 22 is lowered and the presser plate will also be lowered to a position corresponding substantially to that shown in Fig. '7, in which position it will be retained by the guide rods 29. The table 22 is still further lowered, so that a bundle of the unperforated boards may be moved onto the table into position to be drilled. The table 22 is then raised until the bundle is engaged by the presser plate 28, and a continued upward movement causes the compression of the plaster-board bundle between the table top and presser plate. this pressure being maintained by the springs 30 while the table is being raised sufficiently to drill the perforations completely through the bundle. The table is then lowered and the resilience of the rollers will raise the bundle slightly and allow it to be easily removed.

A peculiar type of drill is desirable in orderthat the perforations may be clean-cut in each be crushed or the fabric torn. For this purpose, the drills 21 are of the twist-drill type and provided with rather large flutes or grooves 37 having the usual side-cutting edges 38, each of these grooves being provided at its lower edge with an angularly disposed cutting edge 39 and a clearance portion 40. A comparatively small unthreaded tapered center point 41 is provided and the land or raised portions of the drill are extended downwardly to provide arcuate cutting lips 42 on each side. This construction provides a drill which will cut a smooth, clean hole through paper coverings of the boards as well as through the entire bundle and which may be repeatedly resharpened for continued use. The walls and 'edges of the perforation will be cleanly and smoothly cut in advance of the drilling.

By the above described arrangement, no change whatsoever need be made in the usual practice or machines for manufacturing the plaster-board lath, and the perforations being made subsequently and with the lath in bundle form ready for shipment it is possible for the manufacturer to provide either kind of board, plain or perforated, from a single type of plaster board machine, as may be demanded by the trade.

perforated plaster-board lath secured to said supporting members, and a plaster coating on the face of said lath and extending into and through said perforations therein, the perforations of said lath extendingcompletely therethrough and being of such size and spacing that they are completely filled with portions of the plaster of said plaster coating in the normal acts of applying said coating to form keys which protrudebeyond and engage with the inner face of the board to form heads bonding the plaster coat to the lath when the plaster sets, the size of each key and the area of-plaster supported thereby being cor-- related to retard calcination of the keys considerably beyondthat of the plaster coating when the construction is subjected to continued high tempertures and to provide an area of'the coating supported by each key sufiiciently large to provide spaced rows of uniformly positioned perforations, said rows being positioned to avoid the supporting members spaced at standard distances when the boards are supported thereon in normal adjacent aligned or staggered relation, and the perforations being of a number and distribution not materially to weaken the board in any direction 2. A fire-resistant plaster wall construction comprising, in combination, supporting members, a perforated plaster-board lath secured to said supporting members and forming a base 'for a'plaster' coating, and a plaster coating applied to the face of said lath and supported there- 'by and penetrating through the perforations therein to an extent suflicient to protrude thus forming keys on the side of the lath opposite said coating, the perforations in said lath being of such size that in the normal acts of plastering they are completely filled with plaster to form said keys which protrude beyond and engage with the inner face of the lath to form heads at the back thereof thereby to lock the plaster coat to the lath when the plaster sets, said'perforations also being small enough to prevent excessive droppings of plaster at the back on a vertical wall and large enough to retard'calcination of 0 avoid the supporting members, and in such 1 number as not unduly to weaken the lath in any direction. 7

3. A fire-resistant plaster wall construction comprising, in combination, supporting members, perforated plaster-board lath secured to said members and a plaster coating applied to the face of the lath and supported thereby, the plaster passing through said perforations in the act of plastering and completely filling the same to form keys and protruding beyond and forming heads on the keys at the opposite side of the lath, the perforations being sufficient large relatively to the thickness of the plaster coating to retard calcination of the keys beyond that of the plaster coating in case of fire, and the area of plaster surrounding each perforation and key being large relatively to the area of the perforation but within the plaster-retaining limi after its calcination.

4. A fire-resistant wall construction comprising, in combination, supporting members, perforated plaster-board lath secured to said members and a plaster coating applied to the face of the lath and supported thereby, said coating penetrating the perforations in the normal act of plastering and completely filling the same and protruding beyond and forming heads at the back of thelath without excessivedroppings in ing away of the calcined plaster from said board.

the case of a vertical wall and thus keying the plaster to the lath, the size of the perforations and their spacing being such that the plaster required therefor is less than ten percent. of the total plaster used.

5. A fire-resistant wall structure of the character described comprising a perforated plasterboard support having 'a heavy fabric coating on each side, a plaster coating applied to one side of said plaster board and substantially thicker than the support, the perforations in said plaster-board support being of a diameter approximately twice the thickness of said support and symmetrically spaced each of the symmetrical outlines formed by adjacently positioned perforations having an area- .of approximately thirty-six times the cross-sectional area of a single perforation, said plaster completely filling said holes and extending beyond and overlapping said support to form a mechanical bond thereto and a seal therewith suiiicient to prevent the admission of air between said plaster coating and said support when the structure is exposed to extreme high temperatures.

6. A plaster-board lath of the character described comprising a comparatively thin plaster board having a set cementitious core and a paper covering adhering thereto, said lath having perporations therethrough, said perforations having a diameter of approximately twice the thick-.

ness of the lath and symmetrically spaced to provide an area between any four adjacent perforations in the same lath and between any two perforations of an adjacent lath and any two of the same lath of approximately thirty-six times the cross-sectional area of the perforations.

'7. A plaster-board lath of the character described comprising a comparatively thin plasterboard having a set cementitious core and a paper covering adhering thereto, said lath having perforations therethrough, said perforations having a diameter of approximately twice the thickness of the lath and symmetrically spaced, each of the symmetrical outlines formed by adjacently positioned perforations having an area of approximately thirty-six times the cross-sectional area of a single perforation.

8. A plaster-board lath consisting of a set cementitious core and fabric sheets adhering to both sides thereof, the said board being provided with perforations drilled therethrough, said perforations having a diameter of approximately three-fourths of an inch and being spaced not less than approximately four inches from center to center of said perforations, whereby sufllcient imperforate areas remain for adherence of calcined plaster when a structure embodying said board is subjected to fire and sufficient keys in uncalcined condition remain to prevent the falling away of thecalcined plaster from said board.

9. A plaster-board lath consisting of a set gypsum core and fabric sheets adhering to both sides thereof, the said board being provided with perforations drilled therethrough, said perforations having a diameter of approximately three-fourths of an inch and being spaced not less than approximately four inches from center to center of said perforations, wher by u ic en imperforate areas remain for adherence of calcined plaster when a structure embodying said board is subjected to fire and suflicient keys in uncalcined condition remain to prevent the fall- 10. A plaster-board lath consisting of a set gypsum core and paper sheets adhering to both sides thereof, the said board being provided with perforations drilled therethrough, said perforations having a diameter of approximately threefourths of an inch and being spaced not less than approximately four inches from center to center of said perforations, whereby sufficient imperforate areas remain for adherence of calcined plaster when a structure embodying said board is subjected to fire and sufllcient keys in uncalcined condition remain to prevent the falling away of the calcined plaster from said board for a sufficient time to meet the requirements of standard fire test conditions.

11. A plaster-board lath comprising an interior core of set cementitious material, layers of heavy paper adhering to'both sides and the edges of said board, said board being provided with perforations formed therein, said perforations being approximately three-fourths of an inch in diameter and so spaced as to leave an area of approximately sixteen square inches of imperiorate area between any four adjacent perforations in said board, none of said perforations being closer than approximately two inches to the edge of said board.

12. A fireproof wall construction comprising a base of perforated plaster-board lath having relatively large perforations whose total area is approximately one-thirty-sixth that of the area of said lath, means for supporting said board, and

a plaster coating on said lath, said coating being at least equal to the thickness of said lath, with the plaster extending entirely through and slightly beyond said perforations so as to form a rivetlike key between the plaster and said lath, whereby when said construction is subjected to fire the dropping of the plaster calcined by the heat of the fire will be prevented, said construction being characterized by withstanding an active confiagration for a period suflicient to meet the requirements of standard fire tests.

13. A plaster-board lath comprising a cementitious core having a fabric facing on each side and a plurality of relatively large perforations therethrough, said perforations being in rows and said rows being parallel with each other and with the edges of said board, the rows adjacent the edges of the board being spaced therefrom approximately one-half of the distance between the perforations in any single row, whereby when a plurality of lath are placed adjacent each other on standard supports spaced on dimensions which are multiples of the distance between the perforations in a row, all of the supports will be between perforations.

14. A plaster-board lath comprising a cementitious core having a fabric facing on each side and a plurality of relatively large perforations therethrough, said perforations being of a diameter approximately twice the thickness of the board, and said perforations being in rows and said rows being parallel with each other and with the edges of said board, the rows adjacent the edges of the board being spaced therefrom approximately one-half of the distance between the perforations in any single row, whereby when a plurality of lath are placed adiacent each other on standard supports spaced on dimensions which are multiples of the distance between the perforations in a row, all of the supports will be between perforations.

15. A plaster-board lath comprising a cementitious core having a fabric facing on each side and a plurality of perforations therethrough, said perforations being of a diameter approximately twice the thickness of the board, andsaid perforations being in rows and said rows being parallel with each other and with the edges of said board, the rows adjacent the edges of the board being spaced therefrom approximately onehalf of the distance between the perforations in any single row, whereby when a plurality of lath are placed adjacent each other on standard supports spaced on dimensions which are multiples of the distance between the perforations in a row, all of the supports will be between perforations, the area between any four adjacent perforations being approximately thirty-six times the area of a perforation.

16. A plaster-board lath comprising a cementitious core having a fabric facing on each side and a plurality of relatively large perforations therethrough, said perforations being in rows and said rows being parallel with each other and with the longitudinal edges of said board, the rows adjacent the longitudinal edges of the board being spaced therefrom approximately one-half of the distance between the perforations in any single row, the rows being so positioned that when a plurality of lath are placed adjacent each other on standard supports spaced on dimensions which are multiples of the distance between the perforations in a row,-all of the supports will be between perforations.

1'7. A plaster-board lath comprising a cementitious core having a fabric facing on each side and a plurality of relatively large perforations therethrough, said perforations being in horizontal and vertical rows and said rows being parallel with each other and said horizontal rows being parallel with the edges of said board, the rows adjacent the edges of the board being spaced therefrom approximately one-half of the distance between the perforations in any single row, and the perforations adjacent the ends of the board being spaced therefrom at least one-half of the distance between adjacent perforations, whereby when a plurality of lath are secured adjacent each other on standard supports spaced on dimensions which are multiples of the distance betweenthe perforations in a row, all of the supports will be between perforations.

18. A plaster-board lath comprising a cementitious core having a paper facing on each side and a plurality of relatively large perforations therethrough, said perforations being spaced rectangularly and in parallel rows, said perforations and said rows being spaced to provide a. distance therebetween not less than three times the diameter of the perforations and in parallel relation to the edges of the board, the rows adjacent the edges of the board being spaced therefrom approximately one-half of the distance between the perforations or one-half of the distance between the rows, whereby when a plurality of the lath are placed adjacent each other on standard supports spaced on dimensions which are multiples of the distance between perforations or rows of adjacent perforations, all rows over the wall surface will be spaced the same distance apart and all of the supports will be between rows.

' 19. A perforated plaster board comprising a set cementitious core, a fabric sheet adhering to one face of said core and folded to enclose parallel edges of the core and overlie the margins of the opposite face, a fabric sheet adhering to the opposite side of said core and overlying said foldedover portions of said first mentioned fabric,'said board being perforated with comparatively few relatively large, clean-cut, smooth bore perforations of such size and distribution as to not weaken the bound edge of the board nor materially weaken the board as a whole and so that no perforations will be closed by standard spaced supports when the board is applied thereto, the size of the perforations and the area between adjacent perforations and between the perforations and said parallel edges being so related as to provide comparatively large, uniform, unperforated areas between adjacent perforations of individual boards and between adjacent perforations of two boards having adjacent folded edges.

20. A laminated perforated plaster board having a set cementitious core and a fabric sheet adhering to each side thereof, a paper binding folded around each longitudinal edge of said core and adhering thereto, said board being perforated with comparatively few relatively large, cleancut, smooth bore perforations of such size and distribution as to not weaken the bound edge of the board nor materially weaken the board as a whole and so that no perforations will be closed by standard spaced supports when the board is applied thereto, the size of the perforations and being spaced from the edges of the board a distance which is half that between the rows of perforations and not smaller than half the width of the supports.

CARLISLE K. B008. 

